1. Field of the Invention
The present invention relates to a pneumatic tire in which a tie bar is provided with a sipeing to enhance on-snow performance and wet performance from middle stage of wear while securing uneven-wear resistance.
2. Description of the Related Art
In a tire such as an all-season tire and snow tire, there is employed a block pattern in which a tread portion is divided into a plurality of blocks by tread grooves including circumferential main grooves extending in the circumferential direction of the tire and lateral grooves intersecting with the circumferential main grooves while taking on-snow performance and wet performance into consideration. At that time, if a tread groove is formed deeply and widely, the performance such as the on-snow performance can highly be secured. On the other hand, the block rigidity is deteriorated, and uneven wear such as heel and toe wear is prone to be generated.
Japanese Patent Application Laid-open No.H11-278016 proposes that the lateral groove is provided with a tie bar which bulges from a bottom surface of the lateral groove, blocks which are adjacent to each other in the circumferential direction of the tire are connected to each other through the tie bar, and the tie bar is formed with a sipeing in a direction of the lateral groove. According to this proposal, since the rigidity of the block in its circumferential direction is enhanced by the tie bar and thus, the uneven wear can be suppressed. The sipeing is exposed from the tread surface from the middle stage of wear, and edge effect is exhibited. Thus, there is a merit that deterioration of the on-snow performance and wet performance caused by the tie bar can be complemented.
However, in a normal sipeing, although the wall surfaces support each other against the force in the circumferential direction of the tire and thus the block rigidity can highly be secured, the wall surfaces can not support each other against the lateral force, and large distortion is generated in the bottom of the sipeing. If the distortion is repeatedly generated, the crack is prone to be generated in the sipeing bottom, and there is a tendency that block becomes cracked.